U.S. patent application number 16/741574 was filed with the patent office on 2020-07-30 for scaling metric for quantifying metrology sensitivity to process variation.
The applicant listed for this patent is KLA Corporation. Invention is credited to Noa Armon, Dana Klein, Tal Marciano.
Application Number | 20200241428 16/741574 |
Document ID | 20200241428 / US20200241428 |
Family ID | 1000004597306 |
Filed Date | 2020-07-30 |
Patent Application | download [pdf] |
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United States Patent
Application |
20200241428 |
Kind Code |
A1 |
Marciano; Tal ; et
al. |
July 30, 2020 |
Scaling Metric for Quantifying Metrology Sensitivity to Process
Variation
Abstract
An overlay metrology system includes a controller to receive,
from an overlay metrology tool, overlay measurements on multiple
sets of overlay targets on a sample with a range of values of a
measurement parameter, where a particular set of overlay targets
includes overlay targets having one of two or more overlay target
designs. The controller may further determine scaling metric values
for at least some of the overlay targets, where the scaling metric
for a particular overlay target is based on a standard deviation of
the overlay measurements of the corresponding set of overlay
targets. The controller may further determine a variability of the
scaling metric values for each of the two or more sets of overlay
targets. The controller may further select, as an output overlay
target design, one of the two or more overlay target designs having
a smallest scaling metric variability.
Inventors: |
Marciano; Tal; (Yokneam,
IL) ; Armon; Noa; (R.D. Misgav, IL) ; Klein;
Dana; (Milpitas, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KLA Corporation |
Milpitas |
CA |
US |
|
|
Family ID: |
1000004597306 |
Appl. No.: |
16/741574 |
Filed: |
January 13, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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62797557 |
Jan 28, 2019 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G03F 7/70491 20130101;
G03F 7/70633 20130101; G06F 17/18 20130101 |
International
Class: |
G03F 7/20 20060101
G03F007/20; G06F 17/18 20060101 G06F017/18 |
Claims
1. An overlay metrology system comprising: a controller configured
to be communicatively coupled with an overlay metrology tool, the
controller including one or more processors configured to execute
program instructions causing the one or more processors to:
receive, from the overlay metrology tool, overlay measurements on
two or more sets of overlay targets on a sample with a plurality of
values of a measurement parameter for configuring the overlay
metrology tool, wherein a particular set of overlay targets
includes overlay targets having one of two or more overlay target
designs; determine scaling metric values for at least some of the
overlay targets in the two or more sets of overlay targets, wherein
the scaling metric for a particular overlay target is based on a
standard deviation of the overlay measurements of the corresponding
set of overlay targets; determine a variability of the scaling
metric values for each of the two or more sets of overlay targets;
and select, as an output overlay target design, one of the two or
more overlay target designs having a smallest scaling metric
variability, wherein the output overlay target design is provided
to one or more fabrication tools to fabricate an overlay target
based on the output overlay target design on a test sample for
measurement with the overlay metrology tool.
2. The system of claim 1, wherein the scaling metric is based on a
weighted standard deviation of the overlay measurements.
3. The system of claim 2, wherein weights of the weighted standard
deviation of the overlay measurements are based on at least one of
contrast or sensitivity of a measurement signal generated by the
overlay metrology tool.
4. The system of claim 1, wherein the scaling metric (S.sub.metric)
is S.sub.metric=.chi., with ovl=.SIGMA..sub.i=1.sup.Novl.sub.i,
where N is a number of the overlay measurements, i is a measurement
parameter index, ovl.sub.i is a value of the overlay measurement
for a measurement parameter index, ovl is a weighted average of the
N overlay measurements, w is a weight for each of the N overlay
measurements, and .chi. is either +1 or -1 and corresponds to a
sign of an asymmetry of an overlay target in the two or more sets
of overlay targets.
5. The system of claim 1, wherein the measurement parameter
comprises: a wavelength of illumination in the overlay metrology
tool.
6. The system of claim 1, wherein the measurement parameter
comprises: a polarization of illumination in the overlay metrology
tool.
7. The system of claim 1, wherein the overlay metrology tool
comprises: an image-based overlay metrology tool.
8. The system of claim 1, wherein the overlay metrology tool
comprises: a scatterometry-based overlay metrology tool.
9. An overlay metrology system comprising: a controller configured
to be communicatively coupled with an overlay metrology tool, the
controller including one or more processors configured to execute
program instructions causing the one or more processors to:
receive, from the overlay metrology tool configured with two or
more hardware configurations, overlay measurements on a set of
overlay targets distributed across a sample with a plurality of
values of a measurement parameter for configuring the overlay
metrology tool; determine scaling metric values for the set of
overlay targets based on the overlay measurements with the two or
more hardware configurations, wherein the scaling metric for a
particular overlay target in the set of overlay target measured
with a particular hardware configuration of the two or more
hardware configurations is based on a standard deviation of the
overlay measurements associated with the particular hardware
configuration; determine a variability of the scaling metric values
associated with each of the two or more hardware configurations;
and select, as an output hardware configuration of the overlay
metrology tool, one of the two or more hardware configurations
having a smallest scaling metric variability, wherein the output
hardware configuration is provided to the overlay metrology tool
for measurement of one or more additional instances of the overlay
target.
10. The system of claim 9, wherein the scaling metric is based on a
weighted standard deviation of the overlay measurements.
11. The system of claim 10, wherein weights of the weighted
standard deviation of the overlay measurements are based on at
least one of contrast or sensitivity of a measurement signal
generated by the overlay metrology tool.
12. The system of claim 9, wherein the scaling metric
(S.sub.metric) is S.sub.metric=.chi., with
ovl=.SIGMA..sub.i=1.sup.Nw.sub.iovl.sub.i, where N is a number of
the overlay measurements, i is a measurement parameter index,
ovl.sub.i is a value of the overlay measurement for a measurement
parameter index, ovl is a weighted average of the N overlay
measurements, w is a weight for each of the N overlay measurements,
and .chi. is either +1 or -1 and corresponds to a sign of an
asymmetry of an overlay target in the set of overlay targets.
13. The system of claim 9, wherein the measurement parameter
comprises: a wavelength of illumination in the overlay metrology
tool.
14. The system of claim 9, wherein the measurement parameter
comprises: a polarization of illumination in the overlay metrology
tool.
15. The system of claim 9, wherein the overlay metrology tool
comprises: an image-based overlay metrology tool.
16. The system of claim 9, wherein the overlay metrology tool
comprises: a scatterometry-based overlay metrology tool.
17. An overlay metrology system comprising: a controller configured
to be communicatively coupled with an overlay metrology tool, the
controller including one or more processors configured to execute
program instructions causing the one or more processors to: receive
a set of site-specific scaling factors to correct overlay
inaccuracy at a set of overlay locations, wherein the site-specific
scaling factors are generated based on overlay measurements of a
set of reference overlay targets distributed at the set of overlay
locations with a plurality of values of a measurement parameter,
wherein the set of reference overlay targets have a common target
design, wherein the set of reference overlay targets include a
known spatial distribution of fabrication errors, wherein the
site-specific scaling factors are based on a standard deviation of
the overlay measurements; receive, at least one test overlay
measurement from at least one overlay target having the common
target design located on at least one location in the set of
overlay locations on a test sample; and correct at least one test
overlay measurement with the corresponding site-specific scaling
factor.
18. The system of claim 17, wherein at least some of the
site-specific scaling factors are based on a weighted standard
deviation of the overlay measurements.
19. The system of claim 18, wherein weights of the weighted
standard deviation of the overlay measurements are based on at
least one of contrast or sensitivity of a measurement signal
generated by the overlay metrology tool.
20. The system of claim 17, wherein the scaling metric
(S.sub.meter) is S.sub.metric=.chi., with
ovl=.SIGMA..sub.i=1.sup.Nw.sub.iovl.sub.i, where N is a number of
the overlay measurements, i is a measurement parameter index,
ovl.sub.i is a value of the overlay measurement for a measurement
parameter index, ovl is a weighted average of the N overlay
measurements, w is a weight for each of the N overlay measurements,
and .chi. is either +1 or -1 and corresponds to a sign of an
asymmetry of an overlay target in the set of reference overlay
targets.
21. The system of claim 17, wherein the measurement parameter
comprises: a wavelength of illumination in the overlay metrology
tool.
22. The system of claim 17, wherein the measurement parameter
comprises: a polarization of illumination in the overlay metrology
tool.
23. The system of claim 17, wherein the overlay metrology tool
comprises: an image-based overlay metrology tool.
24. The system of claim 17, wherein the overlay metrology tool
comprises: a scatterometry-based overlay metrology tool.
25. A method comprising: measuring, on a set of overlay targets
distributed across a reference sample, overlay with a plurality of
values of a measurement parameter for configuring an overlay
metrology tool, wherein overlay targets in the set of overlay
targets have a common target design, wherein the set of overlay
targets have a known spatial distribution of fabrication errors;
determining scaling metric values for the plurality of overlay
targets based on the overlay measurements, wherein the scaling
metric for a particular overlay target of the set of overlay
targets is based on a standard deviation of the overlay
measurements; identifying a metrology recipe including a value of
the measurement parameter providing an insensitivity to the
fabrication errors within a selected tolerance based on a
correlation between the scaling metric values and the measurement
parameter; and measuring overlay on at least one overlay target
having the common target design on a test sample with the
identified metrology recipe.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application claims the benefit The present
application claims the benefit under 35 U.S.C. .sctn. 119(e) of
U.S. Provisional Application Ser. No. 62/797,557, filed Jan. 28,
2019, entitled SCALING METRIC SMETRIC FOR QUANTIFYING METROLOGY
CONFIGURATION'S SENSITIVITY TO PROCESS VARIATION, naming Tal
Marciano, Noa Armon, and Dana Klein as inventors, which is
incorporated herein by reference in the entirety.
TECHNICAL FIELD
[0002] The present disclosure is related generally to overlay
metrology and, more particularly, to evaluating robustness of
overlay metrology to process variations.
BACKGROUND
[0003] Overlay metrology systems typically measure the alignment of
multiple layers of a sample by characterizing an overlay target
having target features located on sample layers of interest.
Further, the overlay alignment of the multiple layers is typically
determined by aggregating overlay measurements of multiple overlay
targets at various locations across the sample. However, the
accuracy and/or repeatability of an overlay measurement of an
overlay target may be sensitive to variations of process parameters
during fabrication of the overlay target and/or measurement
parameters used to inspect a fabricated overlay target. For
example, process parameter variations (e.g., associated with layer
deposition, pattern exposure, etching, or the like) may lead to
deviations of a fabricated overlay target from an intended design
(e.g., asymmetries in sidewall angles, or the like) that may
introduce error into an overlay measurement. By way of another
example, the accuracy of an overlay measurement of a given
fabricated overlay target may vary based on exact values of
measurement parameters associated with an overlay metrology tool
(e.g., wavelength, polarization, or the like). Accordingly, it may
be desirable to provide systems or methods for evaluating the
robustness of overlay target designs.
SUMMARY
[0004] An overlay metrology system is disclosed in accordance with
one or more illustrative embodiments of the present disclosure. In
one illustrative embodiment, the system includes a controller to be
communicatively coupled with an overlay metrology tool. In another
illustrative embodiment, the controller receives, from the overlay
metrology tool, overlay measurements on two or more sets of overlay
targets on a sample with a plurality of values of a measurement
parameter for configuring the overlay metrology tool, where a
particular set of overlay targets includes overlay targets having
one of two or more overlay target designs. In another illustrative
embodiment, the controller determines scaling metric values for at
least some of the overlay targets in the two or more sets of
overlay targets, where the scaling metric for a particular overlay
target is based on a standard deviation of the overlay measurements
of the corresponding set of overlay targets. In another
illustrative embodiment, the controller determines a variability of
the scaling metric values for each of the two or more sets of
overlay targets. In another illustrative embodiment, the controller
selects, as an output overlay target design, one of the two or more
overlay target designs having a smallest scaling metric
variability, wherein the output overlay target design is provided
to one or more fabrication tools to fabricate an overlay target
based on the output overlay target design on a test sample for
measurement with the overlay metrology tool.
[0005] An overlay metrology system is disclosed in accordance with
one or more illustrative embodiments of the present disclosure. In
one illustrative embodiment, the system includes a controller to be
communicatively coupled with an overlay metrology tool. In another
illustrative embodiment, the controller receives, from the overlay
metrology tool configured with two or more hardware configurations,
overlay measurements on a set of overlay targets distributed across
a sample with a plurality of values of a measurement parameter for
configuring the overlay metrology tool. In another illustrative
embodiment, the controller determines scaling metric values for the
set of overlay targets based on the overlay measurements with the
two or more hardware configurations, where the scaling metric for a
particular overlay target in the set of overlay target measured
with a particular hardware configuration of the two or more
hardware configurations is based on a standard deviation of the
overlay measurements associated with the particular hardware
configuration. In another illustrative embodiment, the controller
determines a variability of the scaling metric values associated
with each of the two or more hardware configurations. In another
illustrative embodiment, the controller selects, as an output
hardware configuration of the overlay metrology tool, one of the
two or more hardware configurations having a smallest scaling
metric variability, where the output hardware configuration is
provided to the overlay metrology tool for measurement of one or
more additional instances of the overlay target.
[0006] An overlay metrology system is disclosed in accordance with
one or more illustrative embodiments of the present disclosure. In
one illustrative embodiment, the system includes a controller to be
communicatively coupled with an overlay metrology tool. In another
illustrative embodiment, the controller receives a set of
site-specific scaling factors to correct overlay inaccuracy at a
set of overlay locations. In another illustrative embodiment, the
site-specific scaling factors are generated based on overlay
measurements of a set of reference overlay targets distributed at
the set of overlay locations with a plurality of values of a
measurement parameter, where the set of reference overlay targets
have a common target design, and where the set of reference overlay
targets include a known spatial distribution of fabrication errors.
In another illustrative embodiment, the site-specific scaling
factors are based on a standard deviation of the overlay
measurements. In another illustrative embodiment, the controller
receives, at least one test overlay measurement from at least one
overlay target having the common target design located on at least
one location in the set of overlay locations on a test sample. In
another illustrative embodiment, the controller corrects at least
one test overlay measurement with the corresponding site-specific
scaling factor.
[0007] A method is disclosed in accordance with one or more
illustrative embodiments of the present disclosure. In one
illustrative embodiment, the method includes measuring, on a set of
overlay targets distributed across a reference sample, overlay with
a plurality of values of a measurement parameter for configuring an
overlay metrology tool. In another illustrative embodiment, the set
of overlay targets have a common target design and include a known
spatial distribution of fabrication errors. In another illustrative
embodiment, the method includes determining scaling metric values
for the plurality of overlay targets based on the overlay
measurements, where the scaling metric for a particular overlay
target of the plurality of overlay targets is based on a standard
deviation of the overlay measurements. In another illustrative
embodiment, the method includes identifying a metrology recipe
including a value of the measurement parameter providing an
insensitivity to the fabrication errors within a selected tolerance
based on a correlation between the scaling metric values and the
measurement parameter. In another illustrative embodiment, the
method includes measuring overlay on at least one overlay target
having the common target design on a test sample with the
identified metrology recipe.
[0008] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory only and are not necessarily restrictive of the
invention as claimed. The accompanying drawings, which are
incorporated in and constitute a part of the specification,
illustrate embodiments of the invention and together with the
general description, serve to explain the principles of the
invention.
BRIEF DESCRIPTION OF DRAWINGS
[0009] The numerous advantages of the disclosure may be better
understood by those skilled in the art by reference to the
accompanying figures.
[0010] FIG. 1A is a conceptual view illustrating an overlay
metrology system, in accordance with one or more embodiments of the
present disclosure.
[0011] FIG. 1B is a conceptual view illustrating the overlay
metrology tool, in accordance with one or more embodiments of the
present disclosure.
[0012] FIG. 1C is a conceptual view illustrating the overlay
metrology tool, in accordance with one or more embodiments of the
present disclosure.
[0013] FIG. 2 is a plot of the contrast precision and inaccuracy as
a function of wavelength for a target with asymmetric sidewall
angles induced by process variations, in accordance with one or
more embodiments of the present disclosure.
[0014] FIG. 3A is a plot illustrating the impact of the strength of
sidewall asymmetry on the overlay inaccuracy, in accordance with
one or more embodiments of the present disclosure.
[0015] FIG. 3B is a plot illustrating the impact of the sign of
sidewall asymmetry on the overlay inaccuracy, in accordance with
one or more embodiments of the present disclosure.
[0016] FIG. 4A is a plot of locations of overlay targets
distributed across a sample, in accordance with one or more
embodiments of the present disclosure.
[0017] FIG. 4B is a plot of measured overlay as a function of
wavelength for the overlay targets depicted in FIG. 4A, in
accordance with one or more embodiments of the present
disclosure.
[0018] FIG. 5A is a schematic representation of a distribution of
process-variation-induced asymmetry on features of an overlay
target, in accordance with one or more embodiments of the present
disclosure.
[0019] FIG. 5B is a simulated representation of overlay targets
distributed across the sample depicted in FIG. 5A, where the
shading of each overlay target represents the value of the
S-metric, in accordance with one or more embodiments of the present
disclosure.
[0020] FIG. 6 is a flow diagram illustrating steps performed in a
method for selecting an overlay target design, in accordance with
one or more embodiments of the present disclosure.
[0021] FIG. 7A is a plot of S-metrics for overlay targets having a
first overlay target design distributed across a sample having
process variations, in accordance with one or more embodiments of
the present disclosure.
[0022] FIG. 7B is a plot of S-metrics for overlay targets having a
second overlay target design distributed across a sample having
process variations, in accordance with one or more embodiments of
the present disclosure.
[0023] FIG. 8 is a flow diagram illustrating steps performed in a
method for selecting a hardware configuration of an overlay
metrology tool, in accordance with one or more embodiments of the
present disclosure.
[0024] FIG. 9 is a flow diagram illustrating steps performed in a
method for generating site-specific scaling factors to correct for
site-specific overlay inaccuracies, in accordance with one or more
embodiments of the present disclosure.
[0025] FIG. 10 is a flow diagram illustrating steps performed in a
method for identifying a metrology recipe that is robust to process
variations, in accordance with one or more embodiments of the
present disclosure.
DETAILED DESCRIPTION
[0026] Reference will now be made in detail to the subject matter
disclosed, which is illustrated in the accompanying drawings. The
present disclosure has been particularly shown and described with
respect to certain embodiments and specific features thereof. The
embodiments set forth herein are taken to be illustrative rather
than limiting. It should be readily apparent to those of ordinary
skill in the art that various changes and modifications in form and
detail may be made without departing from the spirit and scope of
the disclosure.
[0027] Embodiments of the present disclosure are directed to
evaluation of the robustness of overlay target designs and/or
recipes for determining overlay based on a selected overlay target
design.
[0028] It is recognized herein that a semiconductor device may be
formed as multiple printed layers of patterned material on a
substrate. Each printed layer may be fabricated through a series of
process steps such as, but not limited to, one or more material
deposition steps, one or more lithography steps, or one or more
etching steps. Further, each printed layer must typically be
fabricated within selected tolerances to properly construct the
final device. For example, the relative placement of printed
elements in each layer (e.g., the overlay) must be well
characterized and controlled with respect to previously fabricated
layers. Accordingly, metrology targets may be fabricated on one or
more printed layers to enable efficient characterization of the
overlay of the layers. Deviations of overlay target features on a
printed layer may thus be representative of deviations of printed
characteristics of printed device features on that layer. Further,
overlay measured at one fabrication step (e.g., after the
fabrication of one or more sample layers) may be used to generate
correctables for precisely aligning a process tool (e.g., a
lithography tool, or the like) for the fabrication of an additional
sample layer in a subsequent fabrication step.
[0029] Overlay metrology is typically performed by fabricating one
or more overlay targets across a sample, where each overlay target
includes features in sample layers of interest, which are
fabricated at the same time as features associated with a device or
component being fabricated. In this regard, overlay errors measured
at a location of an overlay target may be representative of overlay
errors of device features. Accordingly, overlay measurements may be
used to monitor and/or control any number of fabrication tools to
maintain production of devices according to specified tolerances.
For example, overlay measurements of a current layer with respect
to a previous layer on one sample may be utilized as feed-back data
to monitor and/or mitigate deviations of the fabrication of the
current layer on additional samples within a lot. By way of another
example, overlay measurements of a current layer with respect to a
previous layer on one sample may be utilized as feed-forward data
to fabricate a subsequent layer on the same sample in a way that
takes into account the existing layer alignments.
[0030] Overlay targets typically include features specifically
designed to be sensitive to overlay errors between sample layers of
interest. An overlay measurement may then be carried out by
characterizing the overlay target using an overlay metrology tool
and applying an algorithm to determine overlay errors on the sample
based on the output of the metrology tool.
[0031] Overlay metrology tools may utilize a variety of techniques
to determine the overlay of sample layers. For example, image-based
overlay metrology tools may illuminate an overlay target (e.g., an
advanced imaging metrology (AIM) target, a box-in-box metrology
target, or the like) and capture an overlay signal including an
image of overlay target features located on different sample
layers. Accordingly, overlay may be determined by measuring the
relative positions of the overlay target features. By way of
another example, scatterometry-based overly metrology tools may
illuminate an overlay target (e.g., a grating-over-grating
metrology target, or the like) and capture an overlay signal
including an angular distribution of radiation emanating from the
overlay target associated with diffraction, scattering, and/or
reflection of the illumination beam. Accordingly, overlay may be
determined based on models of the interaction of an illumination
beam with the overlay target.
[0032] Regardless of the overlay measurement technique, an overlay
metrology tool is typically configurable according to a recipe
including a set of measurement parameters utilized to generate an
overlay signal. For example, a recipe of an overlay metrology tool
may include, but is not limited to, an illumination wavelength, a
detected wavelength of radiation emanating from the sample, a spot
size of illumination on the sample, an angle of incident
illumination, a polarization of incident illumination, a position
of a beam of incident illumination on an overlay target, a position
of an overlay target in the focal volume of the overlay metrology
tool, or the like. Accordingly, an overlay recipe may include a set
of measurement parameters for generating an overlay signal suitable
for determining overlay of two or more sample layers.
[0033] The accuracy and/or the repeatability of an overlay
measurement may depend on the overlay recipe as well as a wide
range of factors associated with the particular geometry of the
overlay target such as, but not limited to, thicknesses of sample
layers, the sizes of overlay target features, the density or pitch
of overlay target features, or the composition of sample layers.
Further, the particular geometry of overlay targets may vary across
the sample in both predictable and unpredictable manners. For
example, the thicknesses of fabricated layers may vary across the
sample in a known distribution (e.g., a thickness may be expected
to be slightly larger in the center of a sample than along an edge)
or may vary according to random fluctuations associated with
defects or random variations of processing steps. Accordingly, a
particular overlay recipe may not provide the same accuracy and/or
repeatability when applied to all overlay targets of a sample, even
if process variations are within selected fabrication
tolerances.
[0034] An overlay measurement using a given algorithm is typically
performed under an assumption that the overlay target includes
perfectly symmetric features developed on perfectly uniform sample
layers formed from perfectly uniform materials. However, process
variations associated with fabrication of an overlay target may
introduce deviations of a fabricated overlay target from designed
characteristics (e.g., sidewall asymmetries, or the like). For
example, process variations may include variations in the
deposition of film layers, the exposure of patterns on film layers,
etching the exposed patterns on the film layers, and the like. In
this regard, any impact of deviations of a fabricated overlay
target from designed characteristics on the measured signal may be
improperly attributed to overlay error and may thus manifest as
inaccuracies in the overlay measurement.
[0035] Further, it may be the case that, for a given overlay target
and a given overlay algorithm, different metrology recipes (e.g.,
different configurations of the overlay metrology tool) may exhibit
different sensitivity to process errors. Put another way, it may be
possible to identify particular measurement recipes (e.g.,
particular values of wavelength, polarization, or the like used by
an overlay metrology tool to characterize an overlay target) that
are relatively robust to process variations associated with
fabrication of a particular overlay target. In this regard, robust
and accurate overlay measurements may be achieved.
[0036] Inaccuracy associated with overlay metrology may be
generally described as:
Overlay.sub.measured= +.delta.N (1)
where is the physical overlay error (e.g., an alignment error of
one sample layer to another). Further, the inaccuracy may be
defined as a function of a measurement parameter (e.g., associated
with a measurement recipe). For example, overlay inaccuracy may be
generally described as a function of wavelength:
Overlay.sub.measured(.lamda.)= +.delta.N (2)
[0037] In one embodiment, an overlay target is evaluated using a
scaling metric (S-metric) that is sensitive to deviations of a
fabricated overlay target from design characteristics induced by
process variations. In this regard, the S-metric may be used to
evaluate the robustness of a metrology recipe applied to a
particular target. For example, the S-metric may be generated based
on overlay measurements of a target under different measurement
parameters (e.g., different metrology recipes).
[0038] It is contemplated herein that the S-metric may be used in
various ways to facilitate robust overlay metrology. In one
embodiment, the S-metric may facilitate the selection of various
aspects of a metrology recipe (e.g., wavelength, polarization, or
the like) to provide robust measurements on a particular overlay
target, even in the presence of process variations across the
sample. For example, a robust measurement recipe may be
characterized as one that provides .delta.N.fwdarw.0 (e.g., see Eq.
(1)) for a range of likely process variations.
[0039] In another embodiment, the S-metric is evaluated for
multiple instances of an overlay target located at different
locations across the sample. In this regard, the S-metric may
facilitate tuning of the metrology recipe based on the target
location. For example, the S-metric may be evaluated for multiple
instances of an overlay target across a sample with known
spatially-varying process variations to evaluate the robustness of
the overlay measurement. Further, robustness may be evaluated using
any metric. For example, it may be the case that the overlay
inaccuracy is small (e.g., .delta.N.fwdarw.0) over a range of
process variations such that the overlay measurements are free of
systematic errors and are further insensitive to process variations
in this range. By way of another example, it may be the case that
the overlay inaccuracy does not approach zero, but is relatively
stable over a range of process variations (e.g.,
var(.delta.N).fwdarw.0). In this regard, the overlay measurement
may be relatively robust, yet may suffer from systematic errors. In
either case, the S-metric may facilitate the selection of a
metrology recipe within selected design criteria.
[0040] In another embodiment, the S-metric may be evaluated for
multiple overlay targets having different designs and/or different
overlay measurement algorithms to evaluate the relative robustness
of the targets and/or algorithms under consideration. In this
regard, the S-metric may facilitate selection of a robust overlay
target and/or measurement algorithm.
[0041] For the purposes of the present disclosure, an overlay
signal associated with an overlay metrology tool may be considered
to be an output of the overlay metrology tool having sufficient
information to determine an overlay including relative positions of
overlay target features on two or more sample layers (e.g., through
analysis using one or more processors, or the like). For example,
an overlay signal may include, but is not required to include, one
or more datasets, one or more images, one or more detector
readings, or the like.
[0042] As used throughout the present disclosure, the term "sample"
generally refers to a substrate formed of a semiconductor or
non-semiconductor material (e.g., a wafer, or the like). For
example, a semiconductor or non-semiconductor material may include,
but is not limited to, monocrystalline silicon, gallium arsenide,
and indium phosphide. A sample may include one or more layers. For
example, such layers may include, but are not limited to, a resist,
a dielectric material, a conductive material, and a semiconductive
material. Many different types of such layers are known in the art,
and the term sample as used herein is intended to encompass a
sample on which all types of such layers may be formed. One or more
layers formed on a sample may be patterned or unpatterned. For
example, a sample may include a plurality of dies, each having
repeatable patterned features. Formation and processing of such
layers of material may ultimately result in completed devices. Many
different types of devices may be formed on a sample, and the term
sample as used herein is intended to encompass a sample on which
any type of device known in the art is being fabricated. Further,
for the purposes of the present disclosure, the term sample and
wafer should be interpreted as interchangeable. In addition, for
the purposes of the present disclosure, the terms patterning
device, mask and reticle should be interpreted as
interchangeable.
[0043] FIG. 1A is a conceptual view illustrating an overlay
metrology system 100, in accordance with one or more embodiments of
the present disclosure.
[0044] In one embodiment, the overlay metrology system 100 includes
an overlay metrology tool 102 to acquire overlay signals from
overlay targets based on any number of overlay recipes. For
example, the overlay metrology tool 102 may direct illumination to
a sample 104 and may further collect radiation emanating from the
sample 104 to generate an overlay signal suitable for the
determination of overlay of two or more sample layers. The overlay
metrology tool 102 may be any type of overlay metrology tool known
in the art suitable for generating overlay signals suitable for
determining overlay associated with overlay targets on a sample
104. The overlay metrology tool 102 may operate in an imaging mode
or a non-imaging mode. For example, in an imaging mode, individual
overlay target elements may be resolvable within the illuminated
spot on the sample (e.g., as part of a bright-field image, a
dark-field image, a phase-contrast image, or the like). By way of
another example, the overlay metrology tool 102 may operate as a
scatterometry-based overlay metrology tool in which radiation from
the sample is analyzed at a pupil plane to characterize the angular
distribution of radiation from the sample 104 (e.g., associated
with scattering and/or diffraction of radiation by the sample
104).
[0045] Further, the overlay tool may be configurable to generate
overlay signals based on any number of recipes defining measurement
parameters for the acquiring an overlay signal suitable for
determining overlay of an overlay target. For example, a recipe of
an overlay metrology tool may include, but is not limited to, an
illumination wavelength, a detected wavelength of radiation
emanating from the sample, a spot size of illumination on the
sample, an angle of incident illumination, a polarization of
incident illumination, a position of a beam of incident
illumination on an overlay target, a position of an overlay target
in the focal volume of the overlay metrology tool, or the like.
[0046] In another embodiment, the overlay metrology system 100
includes a controller 106 communicatively coupled to the overlay
metrology tool 102. The controller 106 may be configured to direct
the overlay metrology tool 102 to generate overlay signals based on
one or more selected recipes. The controller 106 may be further
configured to receive data including, but not limited to, overlay
signals from the overlay metrology tool 102. Additionally, the
controller 106 may be configured to determine overlay associated
with an overlay target based on the acquired overlay signals.
[0047] In another embodiment, the controller 106 includes one or
more processors 108. For example, the one or more processors 108
may be configured to execute a set of program instructions
maintained in a memory device 110, or memory. The one or more
processors 108 of a controller 106 may include any processing
element known in the art. In this sense, the one or more processors
108 may include any microprocessor-type device configured to
execute algorithms and/or instructions. Further, the memory device
110 may include any storage medium known in the art suitable for
storing program instructions executable by the associated one or
more processors 108. For example, the memory device 110 may include
a non-transitory memory medium. As an additional example, the
memory device 110 may include, but is not limited to, a read-only
memory, a random access memory, a magnetic or optical memory device
(e.g., disk), a magnetic tape, a solid state drive and the like. It
is further noted that memory device 110 may be housed in a common
controller housing with the one or more processors 108.
[0048] FIG. 1B is a conceptual view illustrating the overlay
metrology tool 102, in accordance with one or more embodiments of
the present disclosure. In one embodiment, the overlay metrology
tool 102 includes an illumination source 112 configured to generate
an illumination beam 114. The illumination beam 114 may include one
or more selected wavelengths of light including, but not limited
to, ultraviolet (UV) radiation, visible radiation, or infrared (IR)
radiation.
[0049] The illumination source 112 may include any type of
illumination source suitable for providing an illumination beam
114. In one embodiment, the illumination source 112 is a laser
source. For example, the illumination source 112 may include, but
is not limited to, one or more narrowband laser sources, a
broadband laser source, a supercontinuum laser source, a white
light laser source, or the like. In this regard, the illumination
source 112 may provide an illumination beam 114 having high
coherence (e.g., high spatial coherence and/or temporal coherence).
In another embodiment, the illumination source 112 includes a
laser-sustained plasma (LSP) source. For example, the illumination
source 112 may include, but is not limited to, a LSP lamp, a LSP
bulb, or a LSP chamber suitable for containing one or more elements
that, when excited by a laser source into a plasma state, may emit
broadband illumination. In another embodiment, the illumination
source 112 includes a lamp source. For example, the illumination
source 112 may include, but is not limited to, an arc lamp, a
discharge lamp, an electrode-less lamp, or the like. In this
regard, the illumination source 112 may provide an illumination
beam 114 having low coherence (e.g., low spatial coherence and/or
temporal coherence).
[0050] In another embodiment, the overlay metrology system 100
includes a wavelength selection device 116 to control the spectrum
of the illumination beam 114 for illumination of the sample 104.
For example, the wavelength selection device 116 may include a
tunable filter suitable for providing an illumination beam 114 with
a selected spectrum (e.g., center wavelength, bandwidth, spectral
profile, or the like). By way of another example, the wavelength
selection device 116 may adjust one or more control settings of a
tunable illumination source 112 to directly control the spectrum of
the illumination beam 114. Further, the controller 106 may be
communicatively coupled to the illumination source 112 and/or the
wavelength selection device 116 to adjust one or more aspects of
the spectrum of the illumination beam 114.
[0051] In another embodiment, the overlay metrology tool 102
directs the illumination beam 114 to the sample 104 via an
illumination pathway 118. The illumination pathway 118 may include
one or more optical components suitable for modifying and/or
conditioning the illumination beam 114 as well as directing the
illumination beam 114 to the sample 104. For example, the
illumination pathway 118 may include, but is not required to
include, one or more lenses 120 (e.g., to collimate the
illumination beam 114, to relay pupil and/or field planes, or the
like), one or more polarizers 122 to adjust the polarization of the
illumination beam 114, one or more filters, one or more beam
splitters, one or more diffusers, one or more homogenizers, one or
more apodizers, one or more beam shapers, or one or more mirrors
(e.g., static mirrors, translatable mirrors, scanning mirrors, or
the like). In another embodiment, the overlay metrology tool 102
includes an objective lens 124 to focus the illumination beam 114
onto the sample 104 (e.g., an overlay target with overlay target
elements located on two or more layers of the sample 104). In
another embodiment, the sample 104 is disposed on a sample stage
126 suitable for securing the sample 104 and further configured to
position the sample 104 with respect to the illumination beam
114.
[0052] In another embodiment, the overlay metrology tool 102
includes one or more detectors 128 configured to capture radiation
emanating from the sample 104 (e.g., an overlay target on the
sample 104) (e.g., sample radiation 130) through a collection
pathway 132 and generate one or more overlay signals indicative of
overlay of two or more layers of the sample 104. The collection
pathway 132 may include multiple optical elements to direct and/or
modify illumination collected by the objective lens 124 including,
but not limited to one or more lenses 134, one or more filters, one
or more polarizers, one or more beam blocks, or one or more
beamsplitters. For example, a detector 128 may receive an image of
the sample 104 provided by elements in the collection pathway 132
(e.g., the objective lens 124, the one or more lenses 134, or the
like). By way of another example, a detector 128 may receive
radiation reflected or scattered (e.g., via specular reflection,
diffuse reflection, and the like) from the sample 104. By way of
another example, a detector 128 may receive radiation generated by
the sample (e.g., luminescence associated with absorption of the
illumination beam 114, and the like). By way of another example, a
detector 128 may receive one or more diffracted orders of radiation
from the sample 104 (e.g., 0-order diffraction, .+-.1 order
diffraction, .+-.2 order diffraction, and the like).
[0053] The illumination pathway 118 and the collection pathway 132
of the overlay metrology tool 102 may be oriented in a wide range
of configurations suitable for illuminating the sample 104 with the
illumination beam 114 and collecting radiation emanating from the
sample 104 in response to the incident illumination beam 114. For
example, as illustrated in FIG. 1B, the overlay metrology tool 102
may include a beamsplitter 136 oriented such that the objective
lens 124 may simultaneously direct the illumination beam 114 to the
sample 104 and collect radiation emanating from the sample 104. By
way of another example, the illumination pathway 118 and the
collection pathway 132 may contain non-overlapping optical
paths.
[0054] FIG. 1C is a conceptual view illustrating an overlay
metrology tool 102, in accordance with one or more embodiments of
the present disclosure. In one embodiment, the illumination pathway
118 and the collection pathway 132 contain separate elements. For
example, the illumination pathway 118 may utilize a first focusing
element 138 to focus the illumination beam 114 onto the sample 104
and the collection pathway 132 may utilize a second focusing
element 140 to collect radiation from the sample 104. In this
regard, the numerical apertures of the first focusing element 138
and the second focusing element 140 may be different. In another
embodiment, one or more optical components may be mounted to a
rotatable arm (not shown) pivoting around the sample 104 such that
the angle of incidence of the illumination beam 114 on the sample
104 may be controlled by the position of the rotatable arm.
[0055] As described previously herein, the overlay metrology tool
102 may be configurable to generate overlay signals associated with
overlay targets on the sample 104 using any number of overlay
recipes (e.g., sets of measurement parameters). Further, the
overlay metrology tool 102 may provide rapid tuning of the
measurement parameters such that multiple overlay signals based on
different recipes may be rapidly acquired. For example, the
controller 106 of the overlay metrology system 100 may be
communicatively coupled with one or more adjustable components of
the overlay metrology tool 102 to configure the adjustable
components in accordance with an overlay recipe.
[0056] An overlay recipe may include one or more aspects of the
spectrum of the illumination beam 114 incident on the sample such
as, but not limited to the wavelength (e.g., the central
wavelength), the bandwidth, and the spectral profile of the
illumination beam 114 as measurement parameters. For example, the
controller 106 may be communicatively coupled to the illumination
source 112 and/or the wavelength selection device 116 to adjust the
spectrum of the illumination beam 114 in accordance with an overlay
recipe.
[0057] In one embodiment, the wavelength selection device 116
includes one or more position-tunable spectral filters in which
spectral characteristics of an incident illumination beam 114
(e.g., a center wavelength, a bandwidth, a spectral transmissivity
value or the like) may be rapidly tuned by modifying the position
of the illumination beam 114 on the filter. Further,
position-tunable spectral filters may include any type of spectral
filter such as, but not limited to, a low-pass filter, a high-pass
filter, a band-pass filter, or a band-reject filter.
[0058] For example, a position-tunable spectral filter may include
one or more thin films operating as an edge filter with a
position-tunable cutoff wavelength. In this regard, the cutoff
wavelength may be tuned by modifying the position of the
illumination beam 114 on the filter. For instance, a low-pass edge
filter may pass (e.g., via transmission or reflection) wavelengths
below the cutoff wavelength, whereas a high-pass edge filter may
pass wavelengths above the cutoff wavelength. Further, a band-pass
filter may be formed from a low-pass edge filter combined with a
high-pass edge filter.
[0059] Referring now to FIGS. 2 through 10, a scaling metric
(S-metric) for evaluating the sensitivity of an overlay metrology
target to process variations is described in greater detail.
[0060] As described previously herein, process variations during
the fabrication of an overlay metrology target (and the associated
device features) may result in deviations of a fabricated overlay
target from design characteristics. For example, process variations
in a film deposition step may result in variations in
characteristics of a sample layer such as, but not limited to,
thickness, homogeneity, or refractive index. By way of another
example, variations in an exposure step may include deviations of
an exposed pattern of elements from a designed pattern. By way of
another example, variations in an etching step may result in
deviations of fabricated features from the exposed pattern such as,
but not limited to, side-wall angle asymmetry.
[0061] The impacts of process variations on overlay targets may
generally be divided into two categories: asymmetric variations and
symmetric variations. Asymmetric variations are characterized by an
asymmetry in one or more elements of an overlay target or of the
overlay target as a whole. Examples of asymmetric process
variations include, but are not limited to, asymmetric sidewall
angles, deformations of grating structures, or target noise. In
contrast, symmetric variations include symmetric physical
deviations of a fabricated overlay target from design
characteristics and may include, but are not limited to, variations
of the optical properties or thickness of one or more sample
layers.
[0062] It is contemplated herein that regions of low measurability
(e.g., regions of low contrast in imaging-based overlay or regions
of low sensitivity in scatterometry-based overlay) may suffer from
a strong amplification of overlay inaccuracy, including inaccuracy
induced by process variations. However, different types of
inaccuracy may have different impacts. For example, asymmetric
variations in an overlay target may lead to amplification of the
inaccuracy error, while symmetric variations in an overlay target
may change the recipe performance and/or robustness of the
recipe.
[0063] It is further contemplated herein that the sensitivity of an
overlay measurement algorithm to deviations of an overlay target
induced by process variations may depend on the precise values of
measurement parameters of an overlay metrology tool (e.g., the
overlay metrology system 100) such as, but not limited to, a
wavelength or polarization of illumination of the overlay
target.
[0064] FIG. 2 is a plot 200 of the contrast precision 202 and
inaccuracy 204 as a function of wavelength for a target with
asymmetric sidewall angles induced by process variations, in
accordance with one or more embodiments of the present disclosure.
As illustrated in FIG. 2, in a region of poor contrast precision,
peaking here at 500 nm, there exists a concurrent amplification of
the inaccuracy. In contrast, the impact of sidewall angle
inaccuracy is low at 400 nm and 600 nm. Accordingly, the overlay
measurement is relatively insensitive to the process variations at
400 nm and 600 nm and is therefore robust at these wavelengths.
[0065] Additionally, the strength and the sign of a
process-variation-induced asymmetry of an overlay target, or
element thereof, may have different impacts on the overlay
inaccuracy. FIG. 3A is a plot 300 illustrating the impact of the
strength of sidewall asymmetry on the overlay inaccuracy, in
accordance with one or more embodiments of the present disclosure.
In FIG. 3A, two structures with different amounts of asymmetry are
considered: Asym1 302 and Asym2 304, where Asym2 304 has a stronger
asymmetry of sidewall angles. As illustrated in plot 300, an
increase in the strength of the sidewall angle asymmetry results in
an increase of the overlay inaccuracy in a region of low contrast
precision (here at 500 nm). FIG. 3B is a plot 306 illustrating the
impact of the sign of sidewall asymmetry on the overlay inaccuracy,
in accordance with one or more embodiments of the present
disclosure. In FIG. 3B, two structures with different amounts of
asymmetry are considered: Asym1 308 and Asym2 310, where Asym1 308
and Asym2 310 have opposite signs of the sidewall angle asymmetry.
As illustrated in plot 306, a flip in the sign of the asymmetry
results in a flip of the inaccuracy behavior around the region of
low contrast precision (here at 500 nm), but no change in
strength.
[0066] Referring now to FIGS. 4A and 4B, the spatial distribution
of process variations and their associated impact on overlay
inaccuracy across a sample is described in greater detail. Since
process variations are generally the result of mechanical and/or
optical effects, different process variations typically have
defined signatures associated with a spatial distribution of the
sign and/or magnitude of induced asymmetries on overlay targets
across a sample. For example, the effect of etch on a sample (e.g.,
a wafer) usually contains a radial signature due to the electron
beam, which results in increasing side wall angle asymmetry (e.g.,
in fabricated grating structures) from the center of the wafer to
the periphery of the sample. Based on FIGS. 3A and 3B, this may
lead to better accuracy in the center of a sample and increasing
inaccuracy toward the sample periphery. By way of another example,
the effect of variations in film deposition typically also results
in a radial thickness variation of the thin film, which may induce
a similar inaccuracy signature across the sample.
[0067] FIG. 4A is a plot 400 of locations of overlay targets
distributed across a sample, in accordance with one or more
embodiments of the present disclosure. FIG. 4B is a plot 402 of
measured overlay as a function of wavelength for the overlay
targets depicted in FIG. 4A, in accordance with one or more
embodiments of the present disclosure. In FIGS. 4A and 4B, overlay
targets near the center of the sample, shown as relatively light
shades, exhibit relatively low resonance around 720 nm, whereas
overlay targets near the periphery of the sample, shown as
relatively dark shades, exhibit relatively high resonance around
720 nm. In this regard, the overlay algorithm has a relatively high
.delta.N (see Equations (1) and (2) above). Further, there exists a
sign inversion between the overlay measurements on the top and
bottom of the sample (based on the Field Y values in FIG. 4A),
which indicates a sign flipping of the physical geometrical
asymmetry within the overlay target as a result of process
variations.
[0068] Further, FIGS. 4A and 4B illustrate that the overlay
algorithm is relatively insensitive to the process variations at
wavelengths in the range of approximately 400-500 nm, which is
indicated by the high stability of the overlay measurement
signature in this wavelength region. Accordingly, overlay
measurements in this wavelength region may generally be more
accurate across the sample. For wavelengths in the range of
approximately 500-600 nm, the overlay measurements tend to scale
with the strength of the asymmetry, which indicates a higher
sensitivity to process variation and therefore greater inaccuracy
for measurements in this wavelength region.
[0069] Referring now to FIGS. 5A and 5B, a scaling metric
(S-metric) for evaluating the robustness of an overlay target
and/or algorithm are described in greater detail.
[0070] It is contemplated herein that a metric may be developed
that evaluates the robustness (or alternatively the sensitivity) of
an overlay measurement of a particular overlay target using a
particular overlay algorithm. In one embodiment, an S-metric as
disclosed herein evaluates any variations of overlay measurements
of a particular overlay target using a particular overlay algorithm
in the presence of process variations as a function of measurement
parameters (e.g., parameters of a metrology recipe) such as, but
not limited to, wavelength or polarization. In this regard, a
sensitivity to process variations may manifest as variability of
the measured overlay (or overlay inaccuracy) as illustrated in
FIGS. 2-5B. For example, FIGS. 2-3B above illustrate that a single
overlay measurement in the presence of a process-variation-induced
deviation of an overlay target is insufficient to distinguish the
impact of the process variation on the overlay measurement.
However, evaluating the overlay measurement (or the overlay
inaccuracy) across a range of measurement parameters (e.g.,
wavelength in the case of FIGS. 2-3B) may allow the impact of the
process variation on the overlay measurement to be determined.
[0071] In one embodiment, the S-metric is calculated as:
S.sub.metric=.chi. (3)
with
ovl=.SIGMA..sub.i=1.sup.Nw.sub.iovl.sub.i (4)
where N is the number of measurements using a different measurement
parameter (e.g., wavelength, polarization, or the like), i is the
measurement parameter index, ovl.sub.i is the value of an overlay
measurement for a given measurement parameter, ovl is a weighted
average of the N overlay measurements, and w is a weight for each
measurement. Further, .chi. may take the value of .+-.1 and may
correspond to a sign of a resonance (e.g., a sign of an asymmetry).
For example, the sign of .chi. may be determined by taking the sign
of the difference between an overlay measurement at or near a
resonance and an overlay measurement far from the resonance.
[0072] In a general sense, the S-metric is based on a weighted
standard deviation of the overlay measurements across a range of
values of a measurement parameter. In this regard, the S-metric may
provide a measure of the variability of the overlay measurements
across the range of measurement parameters.
[0073] It is contemplated herein that the formulation of the
S-metric in Equations (3) and (4) provides substantial flexibility
for implementation. For example, the absolute value of the S-metric
may be of particular interest in applications where the particular
sign of the S-metric (e.g., the value of .chi.) may be disregarded.
By way of another example, the overlay variability over the
different measurements may be evaluated using different methods
(e.g., the standard deviation weighted or not, integral, and the
like).
[0074] In one embodiment, the weights w are determined based on a
selected quality metric associated with the overlay measurements
such as, but not limited to, contrast (e.g., in image-based
overlay), sensitivity (e.g., in scatterometry-based overlay). In
this regard, the impact of noise may be mitigated. In another
embodiment, the weights w are all set to be equal (e.g., 1) to
provide an unweighted metric.
[0075] FIG. 5A is a schematic representation of a distribution of
process-variation-induced asymmetry on features of an overlay
target, in accordance with one or more embodiments of the present
disclosure. In FIG. 5A, features of overlay targets 502 near the
center of a sample 504 may have relatively little to no asymmetry.
However, features of overlay targets 502 exhibit increasingly
strong sidewall angle asymmetry of one sign in positions
progressing towards the upper right portion of the sample (in the
orientation of FIG. 5A) and increasingly strong sidewall angle
asymmetry of an opposite sign in positions progressing towards the
lower left portion of the sample. FIG. 5B is a simulated
representation of overlay targets 502 distributed across the sample
504 depicted in FIG. 5A, where the shading of each overlay target
502 represents the value of the S-metric, in accordance with one or
more embodiments of the present disclosure.
[0076] As illustrated in FIG. 5B, the S-metric of overlay targets
distributed across a sample 504 in the presence of process
variations (here, sidewall angle asymmetry) allows for an
evaluation of the sensitivity of the overlay landscape (an overlay
algorithm applied to an overlay target over a range of measurement
recipe parameters).
[0077] Referring now to FIGS. 6 through 10, the S-metric may be
applied in numerous ways to facilitate accurate and robust overlay
metrology.
[0078] FIG. 6 is a flow diagram illustrating steps performed in a
method 600 for selecting an overlay target design, in accordance
with one or more embodiments of the present disclosure. For
example, an overlay target design may be selected out of a series
of candidate target designs based on S-metric calculations to
provide robust overlay metrology. Applicant notes that the
embodiments and enabling technologies described previously herein
in the context of the overlay metrology system 100 should be
interpreted to extend to method 600. It is further noted, however,
that the method 600 is not limited to the architecture of the
overlay metrology system 100.
[0079] In one embodiment, the method 600 includes a step 602 of
performing overlay measurements on two or more sets of overlay
targets on a sample with a plurality of values of a measurement
parameter of the overlay metrology tool, where a particular set of
overlay targets includes overlay targets having one of two or more
overlay target designs. For example, the different target designs
may have different sizes, orientations, and/or distributions of
features. Further, the target designs may be suitable for
imaging-based overlay measurements or scatterometry-based overlay
measurements.
[0080] The measurement parameters of the overlay metrology tool may
include any parameter associated with a metrology recipe such as,
but not limited to, an illumination wavelength, a detected
wavelength of radiation emanating from the sample, a spot size of
illumination on the sample, an angle of incident illumination, a
polarization of incident illumination, a position of a beam of
incident illumination on an overlay target, or a position of an
overlay target in the focal volume of the overlay metrology
tool.
[0081] In another embodiment, the method 600 includes a step 604 of
determining scaling metric values for at least some of the overlay
targets in the two or more sets of overlay targets, where the
scaling metric for a particular overlay target is based on a
standard deviation of the overlay measurements of the corresponding
set of overlay targets. In one embodiment, the scaling metric
corresponds to the S-metric in Equations (3) and (4). In this
regard, the scaling metric may correspond to a weighted standard
deviation of the overlay measurements, where the weights are
determined based on any quality metric known in the art such as,
but not limited to, contrast or sensitivity. In another embodiment,
the scaling metric corresponds to an unweighted standard deviation
of the overlay measurements.
[0082] In another embodiment, the method 600 includes a step 606 of
determining a variability of the scaling metric values for each of
the two or more sets of overlay targets. In this regard, the
S-metric variability associated with each of the two or more
overlay target designs may be evaluated. The variability may
include any statistical measure of variability known in the art
including, but not limited to, standard deviation, variance, or the
like.
[0083] In another embodiment, the method 600 includes a step 608 of
selecting, as an output overlay target design, one of the two or
more overlay target designs having a smallest scaling metric
variability. In another embodiment, the method 600 includes a step
610 of measuring overlay of a test sample including one or more
overlay targets with the output overlay target design. In this
regard, the output overlay target design selected by method 600 may
be implemented in a production line for the fabrication of one or
more devices.
[0084] FIGS. 7A and 7B illustrate selection of an overlay target
design based on S-metric variability. FIG. 7A is a plot 702 of
S-metrics for overlay targets having a first overlay target design
distributed across a sample having process variations, in
accordance with one or more embodiments of the present disclosure.
FIG. 7B is a plot 704 of S-metrics for overlay targets having a
second overlay target design distributed across a sample having
process variations, in accordance with one or more embodiments of
the present disclosure. Based on FIGS. 7A and 7B, the first overlay
target design has a smaller S-metric variability (e.g., a smallest
3a, or the like) as a function of wavelength. In this regard, the
first overlay target design may provide relatively more robust
overlay measurements.
[0085] It is further contemplated herein that S-metric variability
may be utilized to evaluate and/or select a metrology recipe (e.g.,
a hardware configuration of the overlay metrology tool).
[0086] FIG. 8 is a flow diagram illustrating steps performed in a
method 800 for selecting a hardware configuration of an overlay
metrology tool, in accordance with one or more embodiments of the
present disclosure. For example, an overlay target design may be
selected out of a series of candidate target designs based on
S-metric calculations to provide robust overlay metrology.
Applicant notes that the embodiments and enabling technologies
described previously herein in the context of the overlay metrology
system 100 should be interpreted to extend to method 800. It is
further noted, however, that the method 800 is not limited to the
architecture of the overlay metrology system 100.
[0087] In one embodiment, the method 800 includes a step 802 of
performing, with an overlay metrology tool configured with two or
more hardware configurations, overlay measurements on a set of
overlay targets distributed across a sample with a plurality of
measurement parameters of the overlay metrology tool.
[0088] The measurement parameters of the overlay metrology tool may
include any parameter associated with a metrology recipe such as,
but not limited to, an illumination wavelength, a detected
wavelength of radiation emanating from the sample, a spot size of
illumination on the sample, an angle of incident illumination, a
polarization of incident illumination, a position of a beam of
incident illumination on an overlay target, or a position of an
overlay target in the focal volume of the overlay metrology tool.
Further, the different hardware configurations may include any
configurations associated with a metrology recipe. In this regard,
the method 800 may facilitate selection of one or more parameters
of the metrology recipe to be robust to process variations.
[0089] In another embodiment, the method 800 includes a step 804 of
determining scaling metric values for the set of overlay targets
based on the overlay measurements with the two or more hardware
configurations, where the scaling metric for a particular overlay
target in the set of overlay target measured with a particular
hardware configuration of the two or more hardware configurations
is based on a standard deviation of the overlay measurements
associated with the particular hardware configuration. In one
embodiment, the scaling metric corresponds to the S-metric in
Equations (3) and (4). In this regard, the scaling metric may
correspond to a weighted standard deviation of the overlay
measurements, where the weights are determined based on any quality
metric known in the art such as, but not limited to, contrast or
sensitivity. In another embodiments, the scaling metric corresponds
to an unweighted standard deviation of the overlay
measurements.
[0090] In another embodiment, the method 800 includes a step 806 of
determining a variability of the scaling metric values associated
with each of the two or more hardware configurations. In this
regard, the S-metric variability associated with each of the two or
more overlay target designs may be evaluated. The variability may
include any statistical measure of variability known in the art
including, but not limited to, standard deviation, variance, or the
like.
[0091] In another embodiment, the method 800 includes a step 808 of
selecting, as an output hardware configuration of the overlay
metrology tool, one of the two or more hardware configurations
having a smallest scaling metric variability. In another
embodiment, the method 800 includes a step 810 of measuring overlay
of an additional instance of the overlay target using the overlay
metrology tool with the output hardware configuration.
[0092] In some embodiments, the evaluation of S-metrics for overlay
targets across a sample may be used to develop site-specific
scaling factors to correct a per-site overlay inaccuracy.
[0093] FIG. 9 is a flow diagram illustrating steps performed in a
method 900 for generating site-specific scaling factors to correct
for site-specific overlay inaccuracies, in accordance with one or
more embodiments of the present disclosure. For example, an overlay
target design may be selected out of a series of candidate target
designs based on S-metric calculations to provide robust overlay
metrology. Applicant notes that the embodiments and enabling
technologies described previously herein in the context of the
overlay metrology system 100 should be interpreted to extend to
method 900. It is further noted, however, that the method 900 is
not limited to the architecture of the overlay metrology system
100.
[0094] In one embodiment, the method 900 includes a step 902 of
measuring, on a set of overlay targets distributed across a
reference sample, overlay with a plurality of values of a
measurement parameter, where the set of overlay targets have a
common target design, and where the plurality of overlay targets
include a known spatial distribution of fabrication errors. In
another embodiment, the method 900 includes a step 904 of
determining scaling metric values for the plurality of overlay
targets based on the overlay measurements, where the scaling metric
for a particular overlay target of the plurality of overlay targets
is based on a standard deviation of the overlay measurements. In
another embodiment, the method 900 includes a step 906 of measuring
overlay on at least one overlay target having the common target
design on a test sample. In another embodiment, the method 900
includes a step 908 of generating site-specific scaling factor to
correct overlay inaccuracy at the locations of overlay targets in
the set of overlay targets based on the scaling metric value of
each corresponding overlay target.
[0095] In some embodiments, the scaling metric may be utilized to
optimize a metrology recipe to provide overlay measurements that
are robust to process variations. FIG. 10 is a flow diagram
illustrating steps performed in a method 1000 for identifying a
metrology recipe that is robust to process variations, in
accordance with one or more embodiments of the present disclosure.
For example, an overlay target design may be selected out of a
series of candidate target designs based on S-metric calculations
to provide robust overlay metrology. Applicant notes that the
embodiments and enabling technologies described previously herein
in the context of the overlay metrology system 100 should be
interpreted to extend to method 1000. It is further noted, however,
that the method 1000 is not limited to the architecture of the
overlay metrology system 100.
[0096] In one embodiment, the method 1000 includes a step 1002 of
measuring, on a set of overlay targets distributed across a
reference sample, overlay with a plurality of values of a
measurement parameter for configuring an overlay metrology tool,
where the set of overlay targets have a common target design, and
where the plurality of overlay targets include a known spatial
distribution of fabrication errors. In another embodiment, the
method 1000 includes a step 1004 of determining scaling metric
values for the plurality of overlay targets based on the overlay
measurements, where the scaling metric for a particular overlay
target of the plurality of overlay targets is based on a standard
deviation of the overlay measurements. In another embodiment, the
method 1000 includes a step 1006 of identifying a metrology recipe
including a value of the measurement parameter providing an
insensitivity to the fabrication errors within a selected tolerance
based on a correlation between the scaling metric values and the
measurement parameter. For example, an accurate measurement
parameter (e.g., an accurate recipe) may be identified based on
calculating: min (S(sites)-ovl.sub.i). In another embodiment, the
method 1000 includes a step 1008 of measuring overlay on at least
one overlay target having the common target design on a test sample
with the identified metrology recipe.
[0097] The herein described subject matter sometimes illustrates
different components contained within, or connected with, other
components. It is to be understood that such depicted architectures
are merely exemplary, and that in fact many other architectures can
be implemented which achieve the same functionality. In a
conceptual sense, any arrangement of components to achieve the same
functionality is effectively "associated" such that the desired
functionality is achieved. Hence, any two components herein
combined to achieve a particular functionality can be seen as
"associated with" each other such that the desired functionality is
achieved, irrespective of architectures or intermedial components.
Likewise, any two components so associated can also be viewed as
being "connected" or "coupled" to each other to achieve the desired
functionality, and any two components capable of being so
associated can also be viewed as being "couplable" to each other to
achieve the desired functionality. Specific examples of couplable
include but are not limited to physically interactable and/or
physically interacting components and/or wirelessly interactable
and/or wirelessly interacting components and/or logically
interactable and/or logically interacting components.
[0098] It is believed that the present disclosure and many of its
attendant advantages will be understood by the foregoing
description, and it will be apparent that various changes may be
made in the form, construction, and arrangement of the components
without departing from the disclosed subject matter or without
sacrificing all of its material advantages. The form described is
merely explanatory, and it is the intention of the following claims
to encompass and include such changes. Furthermore, it is to be
understood that the invention is defined by the appended
claims.
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